(a) Field of the Invention
The present invention relates to control of a converter for an electric vehicle. More particularly, the present invention relates to a control method of a converter for an electric vehicle and a control system thereof for controlling the converter when the converter of the electric vehicle fails.
(b) Description of the Related Art
Generally, an electric vehicle means a vehicle driven only by electricity.
A hybrid vehicle is a vehicle in which functions of a gasoline vehicle and an electric vehicle are combined in order to remedy various drawbacks of the gasoline vehicle and the electric vehicle. Therefore, a driver of the hybrid vehicle can select a gasoline engine drive mode, an electric motor drive mode, and a hybrid mode as occasion demands.
As described above, the electric vehicle includes the hybrid vehicle in a broad sense. Therefore, the electric vehicle in a narrow sense and the hybrid vehicle are called “the electric vehicle” in this specification.
Since petroleum is not used as fuel during the electric motor drive mode in the electric vehicle, exhaust gas does not occur and noise is low.
Meanwhile, the electric vehicle is provided with a converter which converts high voltage generated by a high voltage battery into low voltage. The converter supplies electricity to electric components or charges a low voltage battery when the electric vehicle is driven by an electric motor. A DC-DC converter, which increases or drops voltage, is used as such a converter.
A control system of the converter for the electric vehicle may be associated with the danger that electric components of the electric vehicle can be damaged because of characteristics of the system treating high voltage.
If a wrong output of a PWM (pulse width modulation) signal is detected, the converter is determined to fail and an output of the PWM signal is stopped according to conventional arts. Herein, the wrong output of the PWM signal may occur due to a time delay of a circuit or failure of a CPU. If the PWM signal is not output, the converter is stopped and function of the electric vehicle is also stopped. If the function of the electric vehicle is stopped during driving, fuel consumption of the vehicle and driver's satisfaction may deteriorate.
In addition, failure control of the converter begins only after the PWM signal is output wrongly. Therefore, the electric components of the vehicle are stressed seriously by high voltage and high current generated due to the wrong output of the PWM signal from a point when the converter fails to a point when failure control of the converter is activated.
Therefore, a converter control with high reliability and quick protection function is necessary in order to prevent or minimize damage of the electric components of the vehicle when the converter fails or operates abnormally.
Meanwhile, a current sensor mounted at a high voltage terminal of the converter detects overcurrent due to wrong output of the PWM signal according to conventional arts for determining failure of the converter. If the current sensor detects the overcurrent, it is determined that the converter fails and output of the PWM signal is stopped.
The electric components can be badly damaged due to wrong output of the PWM signal if a current sensor operates sensitively, and output of the PWM signal can be stopped abnormally due to noise of the current sensor if the current sensor operates too sensitively according to conventional arts. To solve such problems, components responding to noise, high precision elements, and a test for obtaining threshold value of overcurrent are necessary. Therefore, research time may be very long and production cost may be high.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.